1. Field of the Invention
The present invention relates to a cooling liquid recirculation system for a light source unit. More particularly the present invention serves to effectively cool a super high voltage mercury-vapor lamp includes a built-in filter used for a photochemical process, and prevents electric shock accidents due to its electrically safe design.
2. Description of Prior Art
Conventionally, ultraviolet rays are irradiated onto a light sensitive material by using a mercury-vapor lamp as a light illuminating tube in order to form an image in the photochemical process. In order to irradiate the wavelengths of light suitable for the light sensitive material, an optical filter is provided separately from the light illuminating tube. For this reason, it is very difficult to prevent elongation/contraction of the object to be projected due to the temperature increases or to prevent the temperature increase of the optical filter due to generated heat. Since a large amount of light is needed for the exposure projection, a large quantity of heat is generated from the light illuminating tube. In order to prevent temperature increases, the light illuminating tube is disposed in a transparent jacket tube through which cooling liquid is recirculated. However, this arrangement does not prevent the temperature increase of the optical filter, which is provided separately from the light illuminating tube, and the elongation/contraction of the irradiated object. According to the invention, in order to solve these problems, a transparent jacket tube through which the cooling liquid is to be recirculated is made of material selected to have an optical filter property for passing wavelengths of light suitable for the light sensitive material, i.e, the irradiated object, and removing wavelengths of light unsuitable for the light sensitive material. Temperature increases of the optical filter and the irradiated object are prevented by recirculating the cooling liquid within the jacket tube.
Conventionally, flowing water or the like is used as the cooling liquid for the jacket tube. However, a large amount of water is needed, and it is difficult to move the equipment because of the water piping system. In addition, it is difficult to control the temperature. Furthermore, if bubbles are formed in the cooling water, the flow resistance is increased, so that the flow is not smooth. As a result, the amount of exposure light is adversely effected.